The long term objective of our studies is to understand the function, disease association, and regulation of the intermediate filament proteins, keratin polypeptides 8, 18, and 19 (K8, K18, and K19). Keratins are expressed in glandular "simple-type" (i.e. single layered) epithelia as found in intestine, liver, and exocrine pancreas. Although the functions of these proteins remain unclear, several blistering/ scaling skin diseases are caused by mutations in the epidermal (non- glandular) keratins, and a K18 mutation was recently identified in a patient with cryptogenic cirrhosis. Key modulators of keratin function are likely to be their posttranslational modifications and associated proteins. A newly identified keratin modification, reported for K18 and K19, is their degradation during apoptosis into stable fragments in association with K8/K18 and K19 hyper-phosphorylation. This degradation occurs at a highly conserved aspartic acid that is found in epidermal and glandular keratins. Of note, two known mutations in the human keratin skin diseases occur in very close proximity to the conserved aspartic acid. Within the above context, this proposal focuses on studying K18 and K19 by testing the hypotheses that: (a) keratin degradation is important for apoptosis progression since one of the main events during apoptosis is remodeling of the cytoskeleton. (b) K18 and K19 coexpression in some digestive epithelia may provide redundant and/or independent functions and (c) K19 phosphorylation and its newly identified interferon-induced associated protein (IFP35) play important regulatory and functional roles. We propose to test our hypotheses by pursuing the following specific aims: (i) Study the biologic significance of K19 fragmentation during apoptosis by specifically inhibiting this fragmentation in cultured cells and transgenic animals. (ii) Study the biologic significance of K19 and K18 fragmentation during apoptosis in cells and tissues where these two proteins are coexpressed. (iii) Study the functional consequences of concurrently disrupting K19 and K18-containing filaments within the same tissues of transgenic mice. (iv) Characterize K19 regulation by phosphorylation. (v) Study the interaction between K19 and the 35 kDa interferon-induced protein, IFP35. Our studies should provide highly relevant information regarding the regulation and biologic significance of glandular keratins and their degradation in digestive-type organs, particularly since several diseases of these organs involve apoptosis. Our proposal may also provide model systems for human disease and for testing potential therapeutic interventions.